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    <title>Document</title>
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    <script>
      //实现一个计数器函数，每次调用该函数返回一个递增的数字
      const createCounter = () => {
        let timer = 0
        return function () {
          timer++
          return timer
        }
      }
      const counter = createCounter()
      console.log(counter())
      console.log(counter())
      console.log(counter())
    </script>
  </body>
</html>
